Rock fracturing method and apparatus for excavation

ABSTRACT

A rock fracturing method and apparatus is disclosed for excavation using hypervelocity projectiles of large mass fired against the rock from a gun using a mixture of a gaseous carbonaceous fuel, such as methane, and oxygen in the gun breech, and detonating the mixture with an electrical spark. The projectiles are formed of concrete with a plastic casing having an annular shear lip.

United States Patent Godfrey 1 Oct. 3, 1972 [54] ROCK FRACTURING METHOD AND APPARATUS FOR EXCAVATION [72] Inventor: Charles S. Godfrey, Berkeley, Calif.

[73] Assignee: Physics International Company, San

Leandro, Calif.

[22] Filed: April 1, 1970 [21] Appl. No.: 24,562

[52] US, Cl ..299/13, 89/1 C, 102/23, 175/45, 175/457, 299/18, 299/64 [51] Int. Cl ..E2lc 37/00 [58] Field of Search 102/22, 23; 89/1 R, 7, l C; 299/13; l75/4.5, 4.57-4.59

[56] References Cited UNITED STATES PATENTS 2,290,851 7/ 1942 Addicks ..299/ 13 X 3,232,168 2/1966 Mangeng et a]. l75/4.57 X 1,585,664 5/1926 Gilman ..299/13 1,241,386 9/1917 Hutton ..299/13 X 1,358,296 11/ 1920 Csanyi ..89/7 1,560,038 ll/l925 Camp ..102/23 Primary Examiner-Ernest R. Purser Attorney-Lindenberg, Freilich & Wasserman [5 7] ABSTRACT A rock fracturing method and apparatus is disclosed for excavation using hypervelocity projectiles of large mass fired against the rock from a gun using a mixture of a gaseous carbonaceous fuel, such as methane, and oxygen in the gun breech, and detonating the mixture with an electrical spark. The projectiles are formed of concrete with a plastic casing having an annular shear lip.

20 Claims, 10 Drawing Figures PATENTED ET 3 I973 3.6 95, 715

SHEET 1 OF 3 Q a Y- CHnQLEs G D REY INVENTOR.

M {WM PATENTEDnms I972 3.695.715

SHEET 3 0F 3 IN VENTOR. (Ii/0245s 6. GooPfieY QT QQJEYS ROCK FRACTURING METHOD AND APPARATUS FOR EXCAVATION BACKGROUND OF THE INVENTION This invention relates to a rock fracturing method and apparatus for rapid excavation.

Techniques which have been developed consist of drilling, blasting, loading and hauling. Machines for loading and hauling broken rock have been developed to adequately serve demands under various operating conditions. Tools and techniques for drilling and blasting have also been improved, and yet sufficiently fast tunneling is still not possible, such as for underground highways and railroads.

A major factor in the time required for tunneling with present techniques is the inherent danger in blast ing and the need to remove all equipment from the blasting area before loading and hauling operations can be resumed. Then drilling operations prepare the site for another blasting. What is required is a technique for tunneling that permits continuous operation in breaking rock out from the tunnel route with concurrent loading and hauling operations.

Boring machines have been developed for excavating tunnels in soft rock, such as shale, with concurrent loading and hauling operations, and low-velocity jet streams of water have been used for rapid excavation in soft materials, such as bituminous coal. Now there is a great need for some technique that will permit continuous operation in tunneling through hard rock.

It has been suggested that tunneling through hard rock be accomplished with hypervelocity jets. Such jets have been produced largely with mechanical systems (compressors, hydraulics, pressure multipliers, pistons, water hammer effects). There seems to be general agreement that the stagnation pressure of the water jet impinging on the rock should be at least ten times the unconfined compressive strength of the rock for effective penetration. Yet most of the apparatus suggested in the past has not met this criterion for many types of silicates or dense ores that might be encountered. Table I shows reported strengths for representative rock types.

TABLE I Number of Average Unconfined Rock Type Varieties Compression Strength Porous Silicate Rock 5 1.0 kbar Granite 5 1.8 kbar Periodite and Others 5 2.0 kbar Quartzite l 4.6 kbar Marble 5 0.8 kbar Limestone 5 1.4 kbar Dolomite 6 2.6 kbar OBJECTS AND SUMMARY OF T HE INVENTION These and other objects of the invention are achieved by use of guns to launch high-velocity solid projectiles of low cost and large mass against the face of rock to be excavated. The guns are spaced a distance from the face to provide space for a continuous rubble removal operation which takes advantage of the manner in which a relatively small quantity of rubble is produced by each of a continuous sequence of shots, and the manner in which damage to rock surrounding the excavation is thus minimized. Successive projectile shots are aimed at optimum distances from prior shots for maximum removal of intermediate structure between an existing crater produced by one shot and a new crater produced by a subsequent shot. To control the damage of shots near the edge of theexcavation, small holes may be drilled'or kerfs may be cut along a line defining the edge of the excavation. An explosive mixture of carbonaceous gas and oxygen is used as an energy source. Once a mixture of oxygen and gas has,

been introduced in the breech of the gun behind the projectile, detonation is ignited'by an electrical spark in the breech.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 illustrate a system for use in vertical excavation.

FIG. 3 illustrates a projectile for use in the system of FIGS. 1 and 2.

FIG. 4 is a graph showing the mass of rock ejected by impacts of projectiles as av function of projectile energy.

FIGS. 5a and 5b. illustrate in plan and elevation views craters formed by successive projectiles at impact points optimally spaced apart.

FIGS. 60 and 6b illustrate in plan and elevation views the control of damage resulting from impact of a projectile with drilled holes.

FIG. 7 illustrates diagrammatically a gun for rapid excavation with high-velocity projectiles in accordance with the present invention.

FIG. 8 illustrates in an isometric view of a system for use in horizontal excavation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, a system is shown for vertical rapid excavation, such as for a silo, in accordance with the present invention which makes use of high-velocity projectiles fired against the face of rock to be excavated at a rate of about 10 shots per tionary beam 13. A winch 14 provides the power for operating the crane.

Once the derrick is positioned, a platform 15 carrying two guns 16 and 17 is lowered until a rotary sweep feeder 18 is resting on the mouth of the pilot hole 11 with a stabilizing post 19 in the hole. To facilitate operations at the beginning of the excavation, the mouth of the pilot hole is widened to a diameter greater than the diameter of the platform, as shown at the top of the excavation illustrated in FIG. 2.

The excavation platform 15 is lowered by means of winches (not shown) mounted on the derrick. By providing a plurality of platform hoisting cables, each connected to a separate winch, a servomechanism can be provided to control the winches and stabilize the platform. The distance between the platform and the sweep feeder 18 may be fixed or adjustable to provide the desired distance between the guns and the face of the rock being excavated, a distance of less than 40 feet.

The guns are powered by an explosive gas mixture from a fuel system 20, preferably methane and oxygen in the ratio of two moles of oxygen to one mole of methane (stoichiometric) injected into the breech of a given gun at a pressure of one-tenth kilobar. Upon ignition by an electrical spark, the pressure increases to 1.5 kilobars, causing a shear lip on a projectile to fail, thereby accelerating the projectile weighing approximately 1 kilogram. In a practical system, the projectiles will have a diameter of cm and be made of inexpensive material. FIG. 3 illustrates a practical projectile comprising a concrete slug 21 cast in a plastic casing 22 having an annular shear lip or flange 23.

The guns are fired automatically at preprogrammed intervals and servo-controlled aiming locations. A manual override control will allow flexibility to the shooting pattern when conditions require it, and an interlock system will prevent a shot being fired into the sweep feeder 18 as it rotates around a column 25. An auger 26 driven by a motor 27 gathers rubble into the column as the feeder sweeps around. A vertical-bucket line conveyor in the column 25 raises the rubble above the platform where it is dropped into a spiral chute 29 that feeds into a bucket through a gate. The bucket is then raised to the surface by means of an overhead hoist mounted on an l-beam 31 and driven horizontally along the beam to dump the rubble into a waiting truck as shown in FIG. I. In practice, a second bucket system will be provided for filling a truck at another station. In that manner, one bucket will be filled with rubble while the other is dumping. The gate in the chute 29 can be automatically closed while the chute is rotated from one bucket-filling station to another.

It should be noted that, with the exception of the guns and the projectiles, the system thus far described for continuous rapid excavation of hard rock employs available equipment used in ways that have been proven in conventional excavation, mining and drilling operations. It should also be noted that other arrangements will readily occur to those skilled in the art, and that an arrangement for horizontal excavation can readily be provided in a manner to be described with reference to FIG. 8 which also provides for continuous removal of rubble to a truck loading station.

Before proceeding with a detailed description of preferred embodiments of the present invention, which involves the use of high-velocity projectiles as jets, the question of whether a jet should have a length-todiameter ratio of several magnitudes or of several orders of magnitude will first be considered. The latter will be referred to as a caliber-l0" jet, where n is a small number, and the former will be referred to as a caliber-n jet, where n is again a small number, such as one.

The acceleration of caliber-n jets can be considered as a purely ballistic problem. A base pressure accelerates a mass whose dimensions are small with respect to the distance a sound signal travels during the time of acceleration. The expansion of hot gases is a classic and highly efficient method of performing such an acceleration. The upper limit of velocity attainable is a function of the sound speed in the expanding gas used. Stagnation pressures attainable from the projectile impact can be much larger than any pressures applied during the acceleration.

For the caliber-l0" jet, however, the acceleration process must be quite different. The mass to be accelerated is so large compared to the cross section area that pushing on the end of the jet column becomes impractical. One method of creating such a jet is by the implosion of a cylindrical or conical liner (i.e., shaped charge). However, these techniques do not appear to be economically attractive. The other method most usually employed to create a caliber-l0" jet is to allow fluid from a high-pressure reservoir to expand through some kind of nozzle. In this case, the stagnation pressures of the resultant steady state jet cannot exceed the pressure in the reservoir. For practical systems, this factor would appear to limit attainable stagnation pressures to less than 10 kbar.

The mechanism for breakage of rock for the two types of jets under consideration is quite different. The caliber-n jet transfers all its energy rapidly to the rock and forms a more or less conventional shallow crater. A large fraction of the volume removed (approximately 50 percent) comes from the spalling off of discrete fragments around the edge of the crater. A good description of the phenomenology of impact crater formation in rock is given by D. E. Gault and E. D. l-Ieitowit in The Partition of Energy for Hypervelocity Impact Craters Formed in Rock, Proceedings of the Sixth Symposium on Hyper-velocity Impact, Volume II, Part 2, (August 1963).

The penetration of a caliber-10" jet is usually explained in terms of a steady-state hydrodynamic concepts derived from an application of Bernoullis equation. The jet applies energy and momentum discretely to the rock for the duration of the jet. The resultant cavity is usually deep and conical in shape.

Since the ratio of stagnation pressure to the strength of the rock appears to be important to rock breakage, a comparison of this parameter for the two types of jets is relevant. Let us assume both jets have a velocity of l.5 km/sec. For purposes of comparison, assume both jets to be water. The stagnation pressure most significant to the caliber-n jet can be obtained by determining the pressure obtained when a plane-wave of water at this velocity impacts a stationary half-plane of rock. This pressure in the case of a water jet is approximately 45 kbar. For the caliber-l jet, there is a very small interval of time when a non-steady pressure of this magnitude exists. As the jet reaches steady state, however, this pressure drops to a value which can be estimated by the following formula:

where p t and p j are the densities of target and jet, V is the velocity of the jet, and U is the velocity at which the interface is receding. Solving this for the assumed impact parameters gives a value of U 0.5 km/sec. and P kbar. For a given jet velocity, therefore, the steadystate conditions of the caliber-l0" jet are much less effective in overcoming the strength of the rock than are the dominant impact conditions of the caliber-n jet.

In view of the foregoing, the present invention employs caliber-n projectiles of large mass (approximately 1 kilogram) impacting rock at roughly 1.5 km/sec. Depending on the material of the projectile, the resulting impacts generate pressures of 45 to 100 kb in hard rock.

A rationale for choosing a large mass projectile comes from examination of impact data. FIG. 4 is a graph of data reported in an article by H. J. Moore, D. E. Gault and E. D. l-leitowit titled Change of Effective Target Strength with Increasing Size of Hypervelocity Impact Craters, in Proceedings of the Seventh Hypervelocity Impact Symposium, Tampa, Florida, Vol. IV, Theory (February 1965). The data shows the mass of rock ejected by impacts of approximately caliber-l projectiles of polyethylene, aluminum and steel into dense competent basalt. The solid line represents least square fit to experimental data, and the dashed line represents theoretical predictions for material with constant strength. The abscissa is the kinetic energy of the projectile corrected for the differences in projectile densities There are also shown by crosses the equivalent data of two impacts at 1.5 km/sec of concrete-nylon projectiles on tombstone quality granite. It can be seen that the ejected mass for concrete-nylon projectiles lies on a line which is increasing as roughly the 1.2 power of energy. For a l,000-gram concrete projectile at 1.5 km/sec the corrected kinetic energy is ergs. The ejected mass would be approximately 60 kilograms. Thus, the rock breakage for impact of 10 ergs is about 60 kg. while the rock breakage for 1,000 impacts of 10 ergs is only [5 kg. Clearly the large mass is far superior, both in terms of breakage mass and breakage rate. Data published by B. W. Vanzant for impacts of steel projectiles into cement at velocities up to 0.3 km/sec Dynamic Rock Penetration Tests at Atmospheric Pressure," Fifth Symposium on Rock Mechanics, (Charles Fairhurst, Ed.), Pergamon Press, New York, New York, pp. 61- 91 1963)), give the following relation:

V= 0.0005 E,,l .25

where V is crater volume (in?) and E, is kinetic energy of projectile (ft.lb.). If roughly the same relation would hold for concrete projectiles, the projectile assumed above would give a crater volume in cement of 7.2 ft. or 500 kg of ejecta.

The increased crater efficiency as a function of increasing energy is probably due to the fact that a large mass of rock has many more potential spall planes for failure than does a small mass. In terms of absolute numbers, tests in dense competent basalt represent a lower limit to the amount of ejecta per shot. Most materials encountered in situ would give substantially higher numbers. The numbers shown in FIG. 1 represent an impact into an infinite half-plane of material. In actual practice, a second shot would be made at a point 30 some optimum distance from the crater 31 of a prior shot as shown in FIGS. 5a and 5b. Some intermediate structure in between the existing crater 11 and a new crater would probably be removed as shown by dotted lines. In a third shot, two such structures might be removed. Successive shots could each count on two such structures. In all, one might count on an average removal of perhaps to 500 kilograms (0.1 1 to 0.55 tons) per shot for hard rock.

In order to localize damage near the edge of a desired excavation, a kerf might be cut or a row 32 of holes may be drilled to define the edge as shown in FIGS. 6a and 6b. A crater 33 produced by a single projectile impacting at a point 34 would have the profile shown in FIG. 6b which is a sectional view along a line normal to the row of holes passing through the impact point 34 of FIG. 6a.

In a preferred embodiment of the present invention, oxygen-methane is used as an energy source, but it should be noted that other energy sources may be used, such as oxygen-propane.

It will be assumed the detonation products have an initial pressure of 1.5 kbar. This should not represent an impossible environment for the barrel 40 of a gun 41 diagrammatically illustrated in FIG. 7 even if transient pressures during detonation exceed that pressure.

A stoichiometric mixture of oxygen and methane has a fifteen-fold pressure increase after detonation. Thus, the gases must be introduced into the breech 42 at approximately one-tenth kbar. Methane is introduced by a pump 43 through a valve 44, and oxygen is introduced by a pump 45 through a valve 46. The pump pressures are selected to provide the desired ratio of gas to oxygen in gram-molecular weight noted hereinbefore.

The gun barrel is assumed to have a 10 cm internal diameter. A projectile 47 made of any solid material which is cheap and can be readily formed into a cylindrical shape is introduced into the breech by a mechanism in accordance with techniques developed for loading military ordnance through a port uncovered upon'removal of a breech-block 49. Projectiles that are relatively stiff and dense (i.e., concrete) are more effective in breaking rock than ductile low density (i.e., plastic) projectiles. The projectile will be held in place against the initial loading pressure by a shear flange 32 or by a tapered shape. Upon detonation through a spark plug 50, the projectile will be released by shearing the flange, or by plastic deformation in the case of a tapered shape for the projectile. The condition of the projectile upon being launched is of little concern as long as it does not fragment in the barrel sufficiently to release the gas pressure.

To guide the front of the projectile 47 into the barrel 40, ridges parallel to the axis of the breech may be provided on the wall of the breech such that the distance from one ridge to another directly opposite will be equal to the diameter of the projectile at the front end.

Corresponding notches would then be provided in the annular sheer lip at the rear end of the projectile. Alternatively, projectiles can be preloaded into a revolving cylinder with several projectile chambers using a suitable cam arrangement to press the revolver against the front end of the breech 42 as another projectile chamber is rotated into firing position.

It should be noted that in the preferred embodiment of the invention approximately 1,500 grams of gas is used per shot (an amount which represents perhaps $0.29 worth of materials as delivered to a site) to break one-tenth to one-half ton of rock. From a point of view of materials, therefore, the present invention competes quite favorably with present techniques. In terms of equivalent energy, it takes from to 50 joules (released by the methane-oxygen combustion) to remove one gram of rock. This compares very favorably to performance of the best drilling techniques (approximately 250 joules/gram).

The shot cycle could be repeated at approximately 10 shots/minute with a rapid-fire breech loading mechanism. This would imply l,500 to 8,000 tons could be removed per 24-hour day. For an S-ft-diameter excavation this would then imply excavating at 400 to 2,000 ft/day. If this is insufficient to saturate any possible scheme for removal of the rock, two or more guns could be employed to increase the breakage rate.

Referring now to FIG. 8, a system is shown in an isometric view for horizontal excavation in accordance with the present invention which makes use of highvelocity projectiles fired against a wall of rock by a pair of guns 51 and 52. Nozzles 53 and 54 are attached to the ends of the guns and connected to pipes 55 and 56 which attach to water hoses at the rear of the guns. Water can then be sprayed on the rubble produced by projectiles fired from the guns to reduce dust in surrounding air. While this is most important in excavating horizontally, the same spray nozzles may also be provided in vertical excavation systems. In each type of excavation, the water tends to form a coarse slurry out of the rubble.

A four wheel vehicle indicated generally by the reference numeral 57 supports the guns on three stanchions 58, 59 and 60. Gimbal rings 61 and 62 are employed to mount the guns on the stanchions such that horizontal pins which support the rings will allow the guns to be independently trained in elevation through separate motors and gear trains. For example, a housing 63 attached to the stanchion 58 includes an electric motor 64 for driving a gear train 65 to position the gun 51 in elevation. Trunnions support the guns in the rings along axes orthogonal to the axes of the guns and the horizontal pins of the rings, such as a trunnion 66 which may be driven to train the gun 51 in azimuth through a motor and gear train in a housing 67 attached to the ring 61. An operator, in a cab indicated generally by the reference numeral 70, can train the guns by actuation of suitable controls conventional in electrical servomechanisms.

The vehicle 57 may be self propelled, but is preferably a tractor-drawn wagon with a tractor hitch at the rear of the vehicle as viewed in FIG. 8. The vehicle is then periodically pushed from the rear to a desired distance from the face of the tunnel being excavated. For that purpose, some or all of the wheels may be adapted with hydraulic means for steering the vehicle from the cab. Once in proper position, the wheels may be locked, again by hydraulic means from the cab. Then a conveyor system designated generally by the reference numeral 71 is driven forward on rol lers, such as roller 72, by hydraulic motors on each side, such as a motor 73. The conveyor system is driven forward sufficiently to place a horizontal scoop 74 at the foot of the wall to be excavated. When the scoop has been loaded sufficiently, it is raised to a near vertical position by hydraulic motors, such as a motor 75 attached to the conveyor belt system. That will dump rubble into a bin 76 having a gate 77 that meters out rubble onto a conveyor belt 78 for removal to the rear of the vehicle. In that regard it should be noted that the conveyor system 71 is substantially longer than the vehicle 57 in order that it reaches a rubble removal system (not shown) in the rear even with the scoop 74 extended to the maximum forward position possible with the motor 73.

Two chutes 81 and 82 with flexible sections 83 and 84 are employed to feed projectiles to the guns from the rear of the cab 70. Standard ordnance techniques may be employed for such a projectile feed system. Alternatively, a preloaded magazine may be mounted on each gun, again using standard ordnance techniques. However, the use of chutes is preferred since it allows greater flexibility in handling the projectiles. For example, the loading system for the chutes may be either manual or automatic with hydraulically actuated push rods synchronized with the breach loading mechanisms of the guns if the force of gravity is not sufficient to overcome friction in the chutes to keep projectiles in the respective breach loading position of each gun.

Two cylinders 85 and 86 are carried on each side for the methane and oxygen used. They may be removable, in order to recharge them, but are preferably recharged periodically, such as every 4 or 8 hours through flexible hoses from larger reservoirs on wagons at a safe distance to the rear.

The major products of methane-oxygen combustion are water, CO and CO. The presence of CO is not itself hazardous if sufficient oxygen is maintained for breathing. The CO can be minimized by burning an oxygen rich mixture. It is possible, however, that operating personnel will prefer to work in an enclosure having a controlled atmosphere, or that safety precautions will require such an enclosure.

Although particular embodiments of the invention have been illustrated and described, using conventional and proven components, it is recognized that modifications and variations may readily occur to those skilled in the art, such as substitution of equivalent conventional and proven components for different operations and functions. Consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is:

1. ln a method for excavation of rock, the improvement comprising positioning a gun in front of rock to be excavated, and from said gun firing large, nonexplosive, mass projectiles having solid heads into selected points of impact on the face of said rock to be excavated for cutting and breaking out of said face some of said rock in and around said point of impact of each projectile where said face includes an area substantially greater than the area of impact by a given projectile, wherein each projectile is propelled to impact said face of rock to be excavated at a point displaced from a crater produced by a previously fired projectile to produce not only breaking of said rock around said point to form another crater but also breakage of rock between the crater thus formed and said crater produced by a previously fired projectile.

2. The improvement defined in claim 1 wherein each projectile is propelled against said face of rock to be excavated with impact pressures ranging from about 45 to about 100 kb.

3. The improvement defined in claim 2 wherein damage is controlled in said rock at the edge of the desired excavation by drilling holes or cutting a kerf into said rock to be excavated in a line defining said edge.

4. In a system for rapid excavation of rock using large mass, nonexplosive projectiles, each having a solid nonpenetrating blunt nose, the combination comprising:

means for continually firing said projectiles at high velocity against selected points on the face of said rock, where said face includes an area substantially greater than the area of impact by a given projectile, to cut and break out of said face some of said rock in and around said area of impact by a given projectile;

means for positioning said firing means a distance from said face to provide working space for removal of rubble; and

means for continually removing rubble while projectiles continue to impact said face.

5. The combination defined in claim 4 wherein each of said projectiles has a ratio of length to diameter approximately equal to one.

6. The combination defined in claim 5 wherein each of said projectiles has a large mass of the order of 1 kg and said firing means imparts a velocity to each of said projectiles of the order of 1.5 km/sec.

7. The combination of claim 6 wherein said firing means comprises:

a gun having a barrel and having a breech adapted to be filled with a mixture of oxygen and a carbonaceous gas; and

valving means for separately filling said breech with said gas at a given pressure and said oxygen at a higher pressure, where said higher pressure is the desired pressure of said mixture, and said lower pressure is selected in proportion to said higher pressure to provide a predetermined ratio of gas to oxygen.

8. The combination of claim 7 including electrical spark means for detonating said mixture in said gun breech.

9. The combination of claim 8 wherein each of said projectiles is held in said barrel of said gun to seal said mixture in said breech by a shear flange at the base thereof.

10. The combination of claim 9 wherein each of said projectiles is comprised of a plastic casing and said shear flange is cast as an integral part of said casing.

11. The combination of claim 10 wherein said casing is filled with low cost, high density material.

12. The combination of claim 11 wherein said matgrial is concrete. I 1 The combination of claim 4 wherein said positioning means comprises a platform for supporting said projectile firing means, and means for lowering said platform into a vertical excavation.

14. The combination of claim 13 wherein said means for removing rubble comprises a continuous vertical conveyor means for continually lifting rubble from the excavation to a position above said platform.

15. The combination of claim 14 wherein said vertical conveyor means passes through the center of said platform and includes a rotary sweep means for gathering rubble into said vertical conveyor means.

16. The combination of claim 15 further including a chute into which said vertical conveyor means discharges rubble, and means for conveying rubble from said chute to a truck load position.

17. The combination of claim 4 wherein said positioning means comprises vehicular means for supporting said projectile firing means, said vehicular means being adapted to be moved into a horizontal excavation.

18. The combination of claim 17 wherein said means for removing rubble comprises a continuous horizontal conveyor means for continually moving rubble from said face of the excavation to a position at the rear of said vehicular means, said rear being at the end of said vehicular means remote from said face of said excavation.

19. The combination of claim 18 wherein said horizontal conveyor means passes beneath said vehicular means and includes means for accumulating rubble and means for actuating said accumulating means to dump accumulated rubble into a feed bin over said conveyor means.

20. The combination of claim 19 including means for positioning said horizontal conveyor means relative to said vehicular means to place said accumulating means at the foot of said face of the excavation. 

1. In a method for excavation of rock, the improvement comprising positioning a gun in front of rock to be excavated, and from said gun firing large, nonexplosive, Mass projectiles having solid heads into selected points of impact on the face of said rock to be excavated for cutting and breaking out of said face some of said rock in and around said point of impact of each projectile where said face includes an area substantially greater than the area of impact by a given projectile, wherein each projectile is propelled to impact said face of rock to be excavated at a point displaced from a crater produced by a previously fired projectile to produce not only breaking of said rock around said point to form another crater but also breakage of rock between the crater thus formed and said crater produced by a previously fired projectile.
 2. The improvement defined in claim 1 wherein each projectile is propelled against said face of rock to be excavated with impact pressures ranging from about 45 to about 100 kb.
 3. The improvement defined in claim 2 wherein damage is controlled in said rock at the edge of the desired excavation by drilling holes or cutting a kerf into said rock to be excavated in a line defining said edge.
 4. In a system for rapid excavation of rock using large mass, nonexplosive projectiles, each having a solid nonpenetrating blunt nose, the combination comprising: means for continually firing said projectiles at high velocity against selected points on the face of said rock, where said face includes an area substantially greater than the area of impact by a given projectile, to cut and break out of said face some of said rock in and around said area of impact by a given projectile; means for positioning said firing means a distance from said face to provide working space for removal of rubble; and means for continually removing rubble while projectiles continue to impact said face.
 5. The combination defined in claim 4 wherein each of said projectiles has a ratio of length to diameter approximately equal to one.
 6. The combination defined in claim 5 wherein each of said projectiles has a large mass of the order of 1 kg and said firing means imparts a velocity to each of said projectiles of the order of 1.5 km/sec.
 7. The combination of claim 6 wherein said firing means comprises: a gun having a barrel and having a breech adapted to be filled with a mixture of oxygen and a carbonaceous gas; and valving means for separately filling said breech with said gas at a given pressure and said oxygen at a higher pressure, where said higher pressure is the desired pressure of said mixture, and said lower pressure is selected in proportion to said higher pressure to provide a predetermined ratio of gas to oxygen.
 8. The combination of claim 7 including electrical spark means for detonating said mixture in said gun breech.
 9. The combination of claim 8 wherein each of said projectiles is held in said barrel of said gun to seal said mixture in said breech by a shear flange at the base thereof.
 10. The combination of claim 9 wherein each of said projectiles is comprised of a plastic casing and said shear flange is cast as an integral part of said casing.
 11. The combination of claim 10 wherein said casing is filled with low cost, high density material.
 12. The combination of claim 11 wherein said material is concrete.
 13. The combination of claim 4 wherein said positioning means comprises a platform for supporting said projectile firing means, and means for lowering said platform into a vertical excavation.
 14. The combination of claim 13 wherein said means for removing rubble comprises a continuous vertical conveyor means for continually lifting rubble from the excavation to a position above said platform.
 15. The combination of claim 14 wherein said vertical conveyor means passes through the center of said platform and includes a rotary sweep means for gathering rubble into said vertical conveyor means.
 16. The combination of claim 15 further including a chute into which said vertical conveyor means discharges rubble, and means For conveying rubble from said chute to a truck load position.
 17. The combination of claim 4 wherein said positioning means comprises vehicular means for supporting said projectile firing means, said vehicular means being adapted to be moved into a horizontal excavation.
 18. The combination of claim 17 wherein said means for removing rubble comprises a continuous horizontal conveyor means for continually moving rubble from said face of the excavation to a position at the rear of said vehicular means, said rear being at the end of said vehicular means remote from said face of said excavation.
 19. The combination of claim 18 wherein said horizontal conveyor means passes beneath said vehicular means and includes means for accumulating rubble and means for actuating said accumulating means to dump accumulated rubble into a feed bin over said conveyor means.
 20. The combination of claim 19 including means for positioning said horizontal conveyor means relative to said vehicular means to place said accumulating means at the foot of said face of the excavation. 